import { chrome, gecko, ie, mac, presto, safari, webkit } from '../util/browser.js';
import { e_preventDefault } from '../util/event.js';

import { updateDisplaySimple } from './update_display.js';
import { setScrollLeft, updateScrollTop } from './scrolling.js';

// Since the delta values reported on mouse wheel events are
// unstandardized between browsers and even browser versions, and
// generally horribly unpredictable, this code starts by measuring
// the scroll effect that the first few mouse wheel events have,
// and, from that, detects the way it can convert deltas to pixel
// offsets afterwards.
//
// The reason we want to know the amount a wheel event will scroll
// is that it gives us a chance to update the display before the
// actual scrolling happens, reducing flickering.

let wheelSamples = 0,
  wheelPixelsPerUnit = null;
// Fill in a browser-detected starting value on browsers where we
// know one. These don't have to be accurate -- the result of them
// being wrong would just be a slight flicker on the first wheel
// scroll (if it is large enough).
if (ie) wheelPixelsPerUnit = -0.53;
else if (gecko) wheelPixelsPerUnit = 15;
else if (chrome) wheelPixelsPerUnit = -0.7;
else if (safari) wheelPixelsPerUnit = -1 / 3;

function wheelEventDelta(e) {
  let dx = e.wheelDeltaX,
    dy = e.wheelDeltaY;
  if (dx == null && e.detail && e.axis == e.HORIZONTAL_AXIS) dx = e.detail;
  if (dy == null && e.detail && e.axis == e.VERTICAL_AXIS) dy = e.detail;
  else if (dy == null) dy = e.wheelDelta;
  return { x: dx, y: dy };
}
export function wheelEventPixels(e) {
  let delta = wheelEventDelta(e);
  delta.x *= wheelPixelsPerUnit;
  delta.y *= wheelPixelsPerUnit;
  return delta;
}

export function onScrollWheel(cm, e) {
  let delta = wheelEventDelta(e),
    dx = delta.x,
    dy = delta.y;

  let display = cm.display,
    scroll = display.scroller;
  // Quit if there's nothing to scroll here
  let canScrollX = scroll.scrollWidth > scroll.clientWidth;
  let canScrollY = scroll.scrollHeight > scroll.clientHeight;
  if (!((dx && canScrollX) || (dy && canScrollY))) return;

  // Webkit browsers on OS X abort momentum scrolls when the target
  // of the scroll event is removed from the scrollable element.
  // This hack (see related code in patchDisplay) makes sure the
  // element is kept around.
  if (dy && mac && webkit) {
    outer: for (let cur = e.target, view = display.view; cur != scroll; cur = cur.parentNode) {
      for (let i = 0; i < view.length; i++) {
        if (view[i].node == cur) {
          cm.display.currentWheelTarget = cur;
          break outer;
        }
      }
    }
  }

  // On some browsers, horizontal scrolling will cause redraws to
  // happen before the gutter has been realigned, causing it to
  // wriggle around in a most unseemly way. When we have an
  // estimated pixels/delta value, we just handle horizontal
  // scrolling entirely here. It'll be slightly off from native, but
  // better than glitching out.
  if (dx && !gecko && !presto && wheelPixelsPerUnit != null) {
    if (dy && canScrollY) updateScrollTop(cm, Math.max(0, scroll.scrollTop + dy * wheelPixelsPerUnit));
    setScrollLeft(cm, Math.max(0, scroll.scrollLeft + dx * wheelPixelsPerUnit));
    // Only prevent default scrolling if vertical scrolling is
    // actually possible. Otherwise, it causes vertical scroll
    // jitter on OSX trackpads when deltaX is small and deltaY
    // is large (issue #3579)
    if (!dy || (dy && canScrollY)) e_preventDefault(e);
    display.wheelStartX = null; // Abort measurement, if in progress
    return;
  }

  // 'Project' the visible viewport to cover the area that is being
  // scrolled into view (if we know enough to estimate it).
  if (dy && wheelPixelsPerUnit != null) {
    let pixels = dy * wheelPixelsPerUnit;
    let top = cm.doc.scrollTop,
      bot = top + display.wrapper.clientHeight;
    if (pixels < 0) top = Math.max(0, top + pixels - 50);
    else bot = Math.min(cm.doc.height, bot + pixels + 50);
    updateDisplaySimple(cm, { top: top, bottom: bot });
  }

  if (wheelSamples < 20) {
    if (display.wheelStartX == null) {
      display.wheelStartX = scroll.scrollLeft;
      display.wheelStartY = scroll.scrollTop;
      display.wheelDX = dx;
      display.wheelDY = dy;
      setTimeout(() => {
        if (display.wheelStartX == null) return;
        let movedX = scroll.scrollLeft - display.wheelStartX;
        let movedY = scroll.scrollTop - display.wheelStartY;
        let sample =
          (movedY && display.wheelDY && movedY / display.wheelDY) ||
          (movedX && display.wheelDX && movedX / display.wheelDX);
        display.wheelStartX = display.wheelStartY = null;
        if (!sample) return;
        wheelPixelsPerUnit = (wheelPixelsPerUnit * wheelSamples + sample) / (wheelSamples + 1);
        ++wheelSamples;
      }, 200);
    } else {
      display.wheelDX += dx;
      display.wheelDY += dy;
    }
  }
}
